IgneousIgneous PetrologyPetrology

John WinterJohn Winter

The Earth’s InteriorThe Earth’s InteriorCrust:Crust:Oceanic crustOceanic crust

Thin: 10 kmThin: 10 km

Relatively uniform stratigraphyRelatively uniform stratigraphy

= = ophiolite suite:ophiolite suite: SedimentsSediments pillow basaltpillow basalt sheeted dikessheeted dikes more massive gabbromore massive gabbro ultramafic (mantle)ultramafic (mantle)

Continental CrustContinental CrustThicker: 20-90 km average ~35 kmThicker: 20-90 km average ~35 km

Highly variable compositionHighly variable composition Average ~ granodioriteAverage ~ granodiorite

The Earth’s InteriorThe Earth’s Interior

Mantle:Mantle:Peridotite (ultramafic)Peridotite (ultramafic)

UpperUpper to 410 km (olivine to 410 km (olivine spinel) spinel) Low Velocity LayerLow Velocity Layer 60-220 km60-220 km

Transition ZoneTransition Zone as velocity increases ~ rapidlyas velocity increases ~ rapidly 660 spinel 660 spinel perovskite-type perovskite-type

SiSiIVIV Si SiVIVI

Lower MantleLower Mantle has more gradual has more gradual velocity increasevelocity increase

Figure 1-2. Major subdivisions of the Earth. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

The Earth’s InteriorThe Earth’s Interior

Core: Core: Fe-Ni metallic alloyFe-Ni metallic alloy

Outer CoreOuter Core is liquidis liquid No S-wavesNo S-waves

Inner CoreInner Core is solidis solid

Figure 1-2. Major subdivisions of the Earth. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.

Figure 1-3. Variation in P and S wave velocities with depth. Compositional subdivisions of the Earth are on the left, rheological subdivisions on the right. After Kearey and Vine (1990), Global Tectonics. © Blackwell Scientific. Oxford.

Figure 1-5. Relative atomic abundances of the seven most common elements that comprise 97% of the Earth's mass. An Introduction to Igneous and Metamorphic Petrology, by John Winter , Prentice Hall.

The Pressure The Pressure GradientGradient P increases = P increases = ghgh Nearly linear through mantleNearly linear through mantle

~ 30 MPa/km~ 30 MPa/km 1 GPa at base of ave crust1 GPa at base of ave crust

Core: Core: incr. more rapidly incr. more rapidly since alloy more densesince alloy more dense

Figure 1-8. Pressure variation with depth. From Dziewonski and Anderson (1981). Phys. Earth Planet. Int., 25, 297-356. © Elsevier Science.

Heat Sources Heat Sources in the Earthin the Earth

1.1. Heat from the early accretion and Heat from the early accretion and differentiation of the differentiation of the

EarthEarth still slowly reaching surfacestill slowly reaching surface

Heat Sources Heat Sources in the Earthin the Earth

1.1. Heat from the early accretion and Heat from the early accretion and differentiation of the differentiation of the

EarthEarth still slowly reaching surfacestill slowly reaching surface

2.2. Heat released by the radioactive Heat released by the radioactive breakdown of unstable nuclidesbreakdown of unstable nuclides

Heat TransferHeat Transfer

1.1. RadiationRadiation

2.2. ConductionConduction

3.3. ConvectionConvection

The Geothermal GradientThe Geothermal Gradient

Figure 1-11(new). Estimates of oceanic (blue curves) and continental shield (red curves) geotherms to a depth of 300 km. The thickness of mature (> 100Ma) oceanic lithosphere is hatched and that of continental shield lithosphere is yellow. Data from Green and Falloon ((1998), Green & Ringwood (1963), Jaupart and Mareschal (1999), McKenzie et al. (2005 and personal communication), Ringwood (1966), Rudnick and Nyblade (1999), Turcotte and Schubert (2002).

The The Geothermal Geothermal

GradientGradient

Pattern of global heat flux variations compiled from observations at over 20,000 sites and modeled on a spherical harmonic expansion to degree 12. From Pollack, Hurter and Johnson. (1993) Rev. Geophys. 31, 267-280.

Cross-section of the mantle based on a seismic tomography model. Arrows represent plate motions and large-scale mantle flow and subduction zones represented by dipping line segments. EPR =- East pacific Rise, MAR = Mid-Atlantic Ridge, CBR = Carlsberg Ridge. Plates: EA = Eurasian, IN = Indian, PA = Pacific, NA = North American, SA = South American, AF = African, CO = Cocos. From Li and Romanowicz (1996). J. Geophys. Research, 101, 22,245-72.

Figure 1-9. Estimated ranges of oceanic and continental steady-state geotherms to a depth of 100 km using upper and lower limits based on heat flows measured near the surface. After Sclater et al. (1980), Earth. Rev. Geophys. Space Sci., 18, 269-311.

Plate Tectonic - Igneous GenesisPlate Tectonic - Igneous Genesis

1.1. Mid-ocean RidgesMid-ocean Ridges

2.2. Intracontinental RiftsIntracontinental Rifts

3. 3. Island ArcsIsland Arcs

4.4. Active ContinentalActive Continental

MarginsMargins

5.5. Back-arc BasinsBack-arc Basins

6.6. Ocean Island BasaltsOcean Island Basalts

7.7. Miscellaneous Intra-Miscellaneous Intra-Continental Continental

ActivityActivity kimberlites, carbonatites, kimberlites, carbonatites,

anorthosites...anorthosites...